1. Field of the Invention
This invention relates to a scale on an apparatus for measuring displacement and more particularly to a scale providing a high environmental resistance on an apparatus for measuring displacement.
2. Related Art of the Invention
A scale on an apparatus for measuring displacement, for example, an electronic caliper disclosed in U.S. Pat. No. 5,973,494 to Karl G. Mareliez et al, is bonded to the top surface of a slider""s beam assembly (denoted as P in FIG. 3A, showing the present invention). Such a the scale includes generally an elongated printed circuit board. A plurality of rectangular gratings 12 are spaced apart along the printed circuit board in an aperiodic pattern on a glass-epoxy substrate 11. The scale includes also a scale cover 30 which is deposited onto the top surface of a plural of rectangular gratings 12 by for example an adhesive tape or the like. The scale cover 30 serves as a protector for the adhesive layer 20. The protector 30 can also include a printed marking.
In such a conventional scale used for an apparatus for measuring displacement, since the top surface side of the scale substrate 11 is formed with raised portions by bonding the rectangular grating 12 thereon, it provides an imperfect contact with the scale cover 30. Consequently contaminated coolant and oil can find their way between the scale member 10 and the scale cover 30 and intrude into the gap therebetween and then the scale cover 30 is easily peeled from the adhesive layer 20. Thereby contaminated coolant and oil cause measurement errors.
Furthermore when such a is scale used in a conventional shop, coolant and oil may potentially intrude into the gap between the scale member 10 and the scale cover 30. In some types of oil and non-water-solvent coolants, chlorine and sulfur may cause chemical reaction with the rectangular grating 12 made from copper to make them corroded, to disrupt the rectangular grating 12 and to result in detection error.
This invention has been made in view of the above-described state of the related art, and has for its object to provide a scale for measuring displacement having a significant resistance to the environment such that it provides great reliability in a harmful industrial environment.